1. Field of the Invention
The present invention relates to a connecting structure for covered wires where their respective conductors are connected to each other by oscillating respective insulating covers of the wires with ultrasonic waves. More particularly, it relates to a connecting structure which is effective to connect a shield wire with a ground wire.
2. Description of the Related Art
Generally, it is complicated and troublesome to handle a shield wire having a braided wire coaxially disposed around a core line (or core lines) with the deteriorated workability in using the shield wire. As an effective measure for improving the deteriorated workability, there is provided a connecting structure for wires which takes advantage of inside heating due to the ultrasonic oscillation by Japanese Unexamined Patent Publication (kokai) No. 7-320842.
In the publication, there are shown two kinds of covered wires. One is a shield wire which comprises a core line, an inside insulating rind arranged outside the core line, a braided wire as a shield conductor arranged outside the inside insulating rind, and an outside insulating rind. The other is a ground wire consisting of a core line and an outside resinous rind arranged outside the core line.
According to the disclosed method of connecting the braided wire of the shield wire being connected to a connector, to the core line of the ground wire being also connected to the connector, in front of the connector, the ground wire is firstly overlaid on the shield wire so as to cross each other at a connection point. Next, the overlapping portions are interposed between upper and lower resin tips. Then, while compressing the upper and lower resin tips from the outside, they are subjected to ultrasonic oscillation by making use of an ultrasonic horn and an anvil. Consequently, both of the outside rinds of the shield wire and the ground wire are molten for elimination, so that the braided wire of the shield wire comes into electrical contact with the core line of the ground wire. Simultaneously, the upper and lower resin tips are mutually welded to each other thereby to seal up the surroundings of the above connecting point. Note, in the modification, there is a case that the upper and lower resin tips are respectively provided, on bearing faces thereof, with wire-accommodating shallow grooves for positioning the shield wire.
However, the above-mentioned connecting structure has a problem that much covering resin, in other words, molten resin which is expected to be removed by the ultrasonic oscillation does remain around a contact between conductors. In such a case, the endurance test against thermal shock etc. would cause the covering resin to be deformed and therefore, the contact between the conductors would be displaced thereby to increase the resistance of the contact disadvantageously. Additionally, there is sometimes observed a phenomenon that, when welding the upper and lower resin tips to each other, the molten covering resin causes the outside insulating rind of the shield to be torn or broken. In such a case, the fixing force between the integrated resin tips and the shield wire, i.e. the strength of connection is lowered with a reduction of insulating effect owing to the integrated tips.